Electron discharge device



June 18, 1946.

J. w. CLARK ELECTRON DISCHARGE DEVICE Filed May 26, 1942 2 She ets-Sheet1 INVENTO)? By J. m CLARK WW 6. ATTORNEY June 18, 1946. J. w. CLARK ELECTRON DISCHARGE DEVICE Filed May 26, 1942 2 Sheets-Sheet 2 INVENTUR J. WCLARK BY ATTORNEY Patented June 18, 1946 2,402,147 ELECTRON DISCHARGEDEVICE John W. Clark, Chatham, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication May 26, 1942 Serial No. 444,517

This invention relates to electron discharge devices and moreparticularly to electron guns for such devices of the velocity variationtype. In velocity variation devices, in general, an electron stream isprojected across a gap or through a region wherein it is subjected to ahigh frequency field and thus is velocity varied. The velocity variedstream then traverses a substantially radio frequency field free regionwherein the velocity variations are converted into density variations bya grouping r bunching of the electrons, and the density varied streamsubsequently traverses a region'or gap in such manner as to deliverenergy to a suitable circuit associated with the latter region or gap.

The degree to which the velocity variations are converted into .densityvariations is dependent upon the extent to which the electrons in thestream are grouped or bunched. In the region where the conversion of thevelocity variations into density variations is effected, space chargeeffects tend to occur, due to theelectrostatic repulsive forces of theelectrons, and such eiiects tend to hinder the grouping or bunching ofthe electrons; Substantial prevention or reduction of these effects hasentailed heretofore material restrictions upon the total current whichcould beutilized with given potentials upon the electrodes or,conversely, has necessitated relatively high electrode potentials formoderate stream currents.

I one general object of thi invention is to improve the efiiciency andoperating characteristics of electron discharge devices ofthe velocityvariation type. More specifically, objects of this invention are to:

j Increase the power obtainable from electron discharge devices of thevelocity variation type;

Decrease the electrode potentials requisite for the realization ofelectron grouping or bunching in an electron stream of a given currentinsuch devices;

Produce efficiently a highly concentrated line focus electron beam; and

"Prevent substantial edge efiects in rent line focus electron beam.

' In one illustrative embodiment of this invention, an electrondischarge device of the velocity variation type comprises electrodesdefining a velocity variation region or gap and adapted to haveassociated therewith a suitable circuit, such as a cavity resonator, oneor both of the electrodes having a narrow, rectangular opening therein,and an electron gun for projecting an electron stream through aidopening. The eleca high our- 4 Claims. (Cl. 250-275) tron gun includes acathode and a beam focusing electrode and an accelerating anodecooperatively associated therewith.

In accordance with one feature of this invention, the electrodesconstituting the electron gun are constructed and arranged to produce aconverging beam of substantially rectangular cross section having a linefocus at substantially the entrance to the velocity varying gap orregion. More specifically, in accordance with one feature of thisinvention, the electrodes constituting the electron gun are made of suchconfiguration and so related that substantially all the electronsemanating from the cathode are concentrated into the beam, includingthose electrons emitted from the lateral extremities of the cathodeemissive surface whereby edge efiects are sub stantially eliminated andhigh operating efiiciencies are realized.

The invention and the aforenoted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of an electron discharge deviceillustrative of one embodiment of this invention, portions of theenclosing vessel and of the collector or target and one of thgapdefining electrodes being broken away to show the construction moreclearly;

Figs. 2 and 3 are longitudinal sectional views of the electron gun,taken at planes at right angles to each other; and

Fig. 4 is an exploded perspective view of the electrodes and otherelements constituting the electron gun. Referring now to the drawings,the electron discharge device illustrated in Fig. 1 is of the velocityvariation type an comprises an enclosing vessel, for example of vitreousmaterial, having bulbous axially aligned end portions It] and II and anintermediate constricted portion l2 joining the end portions. SupportedWithin the end portion Ill, as by a leading-in conductor structure [3afiixed within a metallic thimble l4 hermetically sealed to this endportion, is a generally cup-shaped target or collector electrode I5. Theother end portion ll of the enclosing vessel is provided with aninwardly extending stem I6 from which an electron gun, designatedgenerally as I! and described in detail hereinafter, is supported inaxial alignment with the target or collector electrode 15.

Disposed within the intermediate portion 12 of the enclosing vessel andin axial alignment with the electron gun ll and the target or collectorelectrode [5 are end gap-defining electrodes and an intermediateelectrode 20. The end electrodes include central, rectangularlyapertured tapered portions 2: and 22, respectively, and outer annularportions 23 and 24, respectively, which extend through and are sealedhermetically to the intermediate portion 12 of the enclosing vessel. Theintermediate electrode is hollow and of rectangular cross section and ismounted by a metallic annulus extending through and sealed hermeticallyto the intermediate portion I2 of the enclosing vessel.

The electron gun, as shown in Figs. 2, 3. and 4, constitutes a unitaryassembly including a stepped base or supporting plate 25 which issupported by a plurality of rigid rods or wire members 2'! secured torigid pins 28 embedded in the stem 15. Mounted upon the plate 26, as bya pair of rigid wires 29 affixed thereto, is acathode including a metal,flattened cylindrical shell 3% and a dished end member 3i, the outersurface of which is coated with a thermionic material. The dishedelectron emissive surface of the cathode includes an intermediateportion 32 conforming to a section of a cylindrical surface and endportions 33 conforming to segments of a spherical surface of the same orsubstantially the same radius as the cylindrical surface mentioned.

Within the cathode is a heater element 34 which may be, for example, adouble helical filament coated with a suitable insulating material.

The cathode is encompassed by a flattened these, electrons toward thelongitudinal axis of cylindrical beam forming electrode 35 which isfitted upon one of the stepped portions of the base or supp rting plate25 and secured thereto as by welding. The beam forming electrode 35extends beyond the end of the cathode toward the target or collectorelectrode l3 and the edge thereof includes linear sections 2 6 parallelto the edges of the intermediate portion 32 of the cathode emissivesurface, and oppositely inclined U-shaped end sections 31.

Mounted in cooperative relation with the cathode and the beam formingelectrode 35 is an accelerating anode; which comprises a flatamed.lindrical por on. 38 extending i t th space bounded by the beam formingelectrode and in axial alignment with this electrode. The edge of theaccelerating anode within this space comprises linear sections 33parallel to. the linear edge sections 36 and similar U-shaped endsections 40, inclined toward the. cathode and substantially parallel tothe edge. sections 31. The accelerating anode includes also flangedplate members 41 which, overlie the edge portions 31 of the beam-formingelectrode. Secured to the flattened cylindrical anode portion 33 are apair of bracket members 42 which are affixed, as by rivets 43, toinsulating supports 4,6, such as mica strips. The insulating supports 44are mounted by metallic strips 65, secured to the supports, as by rivets45, and secured also, as by welding, to the base plate 26.

Electrical connection to the cathode, the heater filament and theaccelerating anode may be established through leading-in conductors 41embedded in the press. The beam-forming electrode 35, by virtue of itsconnection to the base plate 26 is operated at cathode potential,although it will be understood that it may be so mounted as to beelectrically separate from the cathode, and thus operable at anysuitable potential relative to. the cathode.

Because of the configuration of the cathode the electron gun so thatedge effects are substantially eliminated and a sharp substantially linefocus beam is obtained.

Realization of optimum or substantially optimum operatingcharacteristics for the electron gun entails a particular design of theelectrodes of the gun. In general, these electrodes may be designed inaccordance with the principles. set forth in Patent 2,268,197, grantedDecember 30, 1941 to John R. Pierce so that substantially all theelectrons emanating from the surface 36, 31 are concentrated into thebeam. In a specific gun of the construction illustrated in Figs. 3. and4, the following dimensions, indicated. in Figs. 2 and 3 and expressedin units, have been found to be very satisfactory. A typical unit isinch.

11:25.0 g==16-.5 m=3'7.5= 13:37.5 h=62.5 7L=6.0 6:441) i=3.1 2 :34.5(1:2.4 76:15.0 1 435 6:6.25 2:3.0 T=15.9 j=35.5

The device illustrated in Fig. 1 is particularly suitable for use as anultra high frequency oscillation generator. Inasmuch as the generalprinciples of operation of similar devices for this purpose are known, adetailed exposition thereof is not necessary. It may be noted briefly,however. that the device shown in Fig. 1 may have a suitably tunedcircuit, such as a cavity resonator, associated with the electrodes 2|,23 and 23, 24. The electron beam. produced by the electron gun isprojected across the gap between the electrodes 20 and 2| and isvelocity varied. As, the beam traverses the path through the: electrode2c, the velocity variations are converted into density; variations and,as a result, electrons areprojected across the gap between theelectrodes 2i) and 22 in bunches or groups so as to deliver energy tothe field within the cavity resonator whereby an oscillating field isestablished and maintained in the resonator.

The device may be used also as. a power amplifier with independentcavities associated with, the two gaps.

It will be noted that in the; device shownin Fig. l the electron beam isa line focus. beam and is of relatively large cross-sectional area ascompared with that of a point. focus beam of the same current magnitude.Hence, in this device, the space charge density within the beam isrelatively small and the electrostatic repulsive forces effective uponthe electrons is correspondingly small. Hencathe bunching, or groupingof the velocity varied electrons requisite for operation of the, devicevcan be realized in devices con.- structed in; accordance with, thisinvention with relatively low voltages on the electrodes for aparticular beam current. Viewed in another way,

in devices constructed in accordance with this invention, highercurrents can be obtained for a given voltage upon the electrodes beforethe space charge forces become sufliciently large to materially preventthe grouping or bunching of the electrons. Thus, the invention enablesthe attainment of both high power and high operating efficiency.

It will be noted also that at the gap between the electrodes 20 and 2|,the beam, although of relatively large cross-sectional area, isextremely thin so that a close coupling between the electrons and theradio frequency fleld at the gap and uniformity of action of the fieldupon the electrons are obtained.

Although a specific embodiment of this invention has been shown anddescribed, it will be understood that it is but illustrative and thatvarious modifications may be made therein without departing from thescope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. An electron gun comprising a cathode having a dished electronemissive surface including an intermediate portion conformingsubstantially to a segment of a cylinder and end portions conformingsubstantially to segments of spheres, a beam-forming electrode having a,flattened cylindrical portion in alignment with said surface and havingan edge in front of said surface which includes intermediate sectionssubstantially parallel to said intermediate portion of said surface andinclined end sections converging away from said surface, and a secondbeam-forming electrode including a flattened cylindrical portion inalignment with and in front of said surface, the edge of said secondflattened cylindrical portion toward said surface including inclined endsections and intermediate sections substantially paralle1 to saidintermediate portion of said cathode.

2. An electron gun comprising a cathode having a dished electronemissive surface including an intermediate portion conformingsubstantially to a segment of a cylinder and end portions conformingsubstantially to segments of spheres, an accelerating anode including ahollow flattened cylindrical portion opposite and in alignment with saidsurface, the edge of said flattened cylindrical portion toward saidsurface including intermediate sections substantially parallel to saidintermediate portion of said cathode and inclined end sections flaringtoward said surface, and a beam-forming electrode having a hollowflattened cylindrical portion encompassing and in alignment with saidcathode and said accelerating anode, the edge of said portion of saidbeamforming electrode in front of said surface including intermediatesections substantially parallel to said intermediate portion of saidsurface and end sections inclined in the same direction as said endsections of said accelerating anode.

3. An electron gun comprising a cathode having a dished electronemissive surface including an intermediate portion conformingsubstantially to a segment of a cylinder and end portions conformingsubstantially to segments of a sphere, said intermediate and endportions having substantially the same radius of curvature, anaccelerating anode having a hollow flattened cylindrical portionopposite and in alignment with said surface, the edge of saidaccelerating anode toward said surface including intermediate sectionssubstantially parallel to said intermediate portion of said cathode andinclined end sections extending toward said surface, and a beam-formingelectrode having a hollow flattened cylindrical portion encompassingsaid cathode and said portion of said accelerating anode and inalignment therewith, the edge of said second flattened cylindricalportion nearest said accelerating anode including inclined end sectionssubstantially parallel to said first end sections and intermediatesections substantially parallel to said intermediate sections of saidaccelerating anode.

4. An electron gun comprising a cathode having an elongated dishedelectron emissive surface including an intermediate substantially linearportion and concave end portions, an accelerating anode including ahollow flattened cylindrical portion opposite and in alignment with saidsurface, the end of said flattened cylindrical portion toward saidsurface including an intermediate portion substantially parallel to saidintermediate portion of said surface and end portions inclined towardsaid surface, and a beamforming electrode including a hollow flattenedcylindrical portion encompassing and in alignment with said cathode andsaid first cylindrical portion, said second cylindrical portion havingan end bounded by an edge including intermediate sections substantiallyparallel to said intermediate portion of said cathode and furtherremoved therefrom than said intermediate portion of said acceleratinganode, said edge including also end sections inclined toward said endportions of said anode.

JOHN W. CLARK.

